The work of Vincent Van Gogh may be among the greatest artistic achievements in human history, but barely a century after his death his work is already starting to fade. The bright yellows of his paintings are turning to a murky brown. But this isn't any ordinary decay - and scientists used a particle accelerator to figure out the previously-unknown chemical reaction that is slowly destroying the works of the Dutch master.

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To solve this chemical mystery, French researchers used the powerful X-rays created by the European Synchrotron Radiation Facility in Grenoble, France. The synchrotron is often used to more closely study the structure of materials, and this particular analysis turned up a most unusual reaction. Sunlight can only penetrate a millionth of a meter into Van Gogh's paintings, but that's enough to trigger a previously unknown reaction that transforms the chrome yellow used in the paintings into a dull brownish color.

This is a particularly big deal for Van Gogh's works, as bright colors and light are so crucial to his compositions. In the late nineteenth century, chrome yellow was one of the newly-available industrial pigments that Van Gogh could use to create incredibly intense, vibrant paintings, most famously seen in his sunflowers paintings.

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But now the sunlight is changing the oxidation state of the chromium in that paint, and this is somehow changing the color from yellow to brown. It's thought that the chromium has a particularly strong reaction when in the presence of compounds containing barium or sulfur, both of which were used in the white paints available in Van Gogh's time. Since Van Gogh often blended white and yellow to create his brightest colors, that could be why his paintings in particular have suffered so much from this reaction.

For now, the best option is to shield Van Gogh's paintings from ultraviolet and sunlight. Researcher Koen Janssens says they still haven't given up hope on restoring Van Gogh's art to its original glory:

"Our next experiments are already in the pipeline. Obviously, we want to understand which conditions favour the reduction of chromium, and whether there is any hope to revert pigments to the original state in paintings where it is already taking place."